If it has been done under an AAN pre EASA then it can be done without a MOD under grandfather rights, ( unless things have changed ) I have done a quick scan through the UK AAN's but cannot see it, it also allows any MOD done by any other Country in EASA as an AAN. I seem to recall some people wanting to fit a prop on some big twin in the Bristol area and the CAA rejecting it until the people found it had been done previously in Italy or the likes and then they had to allow it.
https://www.caa.co.uk/Commercial-ind...pproval-notes/